This is a followup to @SorosFootSoldier@hexbear.net 's recent thread for completeness' sake.
I'll state an old classic that is seen as a genre defining game because it is: Myst. Yes, it redefined the genre... in ways I fucking hated and that the adventure game genre took decades to fully recover from. It was a pompous mess in its presentation and was the worst kind of "doing action does vague thing or nothing at all, where is your hint book" puzzle gameplay wrapped in graphical hype which ages pretty poorly as far as appeal qualities go.
So many adventure games tried to be Myst afterward that the sheer budgetary costs and redundancy of the also-rans crashed the adventure game genre for years.
I feel that way about XVI. It's been a colorful series with horse-birds and over the top summoned demigods and party members with wacky names for a very long time and the attempt to grimdark it up just fell flat for me. It doesn't help that the main inspiration for XVI according to Yoshi-P was Game of Thrones, which I've never liked.